In favor of loops

parsing-long-string.js

function buildObject(str) {
  var newObj = {};
  var len = str.length;
  var at = 1;

  if (str[0] != "{") 
    return null;
    
  if (len < 1) 
    console.log('broke out');

  while (at < len) 
    newObj[ getProperty() ] = getValue();

  return newObj;

  function getProperty() { 
    return getPart(":}")  
  }
  
  function getValue() {  
    return parse( getPart(",}") || null) 
  }
  
  function getPart(terminators) {
    var to = at, part = null;
    while (  to <  len 
          && -1 == terminators.indexOf( str[to] ) 
          )
        to++; 
    part = str.substring(at,to);
    at = to + 1;
    return part
  }
}

//test code:
function parse(s) { return s } //dummy parse function

var resultFor = 
    { "{name:osher,yearOfBirth:1976}" : { name: "osher", yearOfBirth: "1976" }
    , "{name:alex,yearOfBirth:1980"   : { name: "osher", yearOfBirth: "1980" }
    , "{:well well,oups"              : { "":  "well well", oups: null }
    , "{"                             : {}
    , ""                              : null
    };

Object.keys(resultFor).forEach(function(input) {
     assert.deepEqual( buildObject(input), resultFor[input] )
})